const boxes = document.querySelectorAll('.box') 
window.addEventListener('scroll', checkBoxes)
 checkBoxes() 
function checkBoxes() {
 const triggerBottom = window.innerHeight / 5 * 4 
boxes.forEach(box => { 
const boxTop = box.getBoundingClientRect().top
 if(boxTop < triggerBottom) { 
box.classList.add('show') } else { box.classList.remove('show')
 } 
})
}